Humans and most other organisms manifest circadian (daily) rhythms that are controlled by an endogenous biochemical oscillator. Many cellular processes, including cell division, enzyme activity, and gene expression, are timed by this oscillator. These "biological clocks" are important to human physiology. For example, psychiatric and medical studies have shown that circadian rhythmicity is involved in some forms of depressive illness, "jet lag," drug tolerance/efficacy, memory, and insomnia. Therefore, understanding the biochemical mechanism of circadian clocks may lead to procedures which will be useful in the diagnosis and treatment of disorders that are relevant to sleep, mental health, and pharmacology. The salient properties of circadian clocks-24 hour time constant, high precision, temperature compensation-are presently impossible to explain biochemically. Although recent breakthroughs in the field of circadian rhythms have identified a number of proteins that appear to act as clock components, we have only just begun to understand how these components interact functionally with themselves and the environment. In model systems, it has been possible to reset the phase of circadian rhythms by induction of clock protein synthesis at specific phases. This approach has been difficult to accomplish in mammalian systems. The current project will test hypotheses concerning the significance of rhythmic clock protein abundance in mammals by using new methods to introduce proteins directly into cells by peptide-mediated transduction across cell membranes. This technology will allow us to modulate the intracellular concentration of clock proteins in cells, tissue slices, and intact animals. These studies will yield results of theoretical importance, but also have the potential for designing treatments for jet lag, insomnia, and other clock-related disorders. This project is appropriate for the NIMH Exploratory/Developmental Grant (R21) Program because it fulfills all of the following primary criteria: (1) innovative research directions, (2) exploration of approaches that are new to a substantive area, and (3) development of new technologies and methods.